1. The Field of the Invention
The present invention relates to a method and apparatus for perforating the walls of a well bore and, in particular, to a method and apparatus which will provide accurate and controlled perforating of a tubular such that annular pressures between tubulars can be relieved allowing completion of a well and stimulation of multiple zones and/or formations.
2. The Prior Art
Once a well bore has been drilled, utilizing the conventional technique of a drilling string with a drill bit secured to the lower free end, the well is completed by positioning a casing string within the well bore. This increases the integrity of the well bore and provides a path to the surface for the produced fluids. The casing string is normally made up of individual lengths of relatively large diameter metal tubulars secured together by any suitable means, for example screw threads or welds. Conventionally, the casing string is cemented to the well face by circulating cement into the annulus defined between the casing string and the well face. The cemented casing string is subsequently perforated to establish fluid communication between the formations of interest, those containing hydrocarbons, and the interior of the casing string. Perforating has conventionally been performed by means of lowering a perforating gun, having at least one shaped charge positioned within a carrier, down inside the casing string and then firing the charge via wireline control from the surface of the earth. A perforating gun may be constructed to be of any length. The perforating gun is lowered within the casing on wireline or tubing to a point adjacent the zone of interest and the shaped explosive charge is detonated to penetrate or perforate both the casing and the formation. This establishes fluid communication between the cased well bore and the zone of interest. The resulting perforations extend through the casing, cement, and a short distance into the formation. The perforating gun is either removed from the well bore or dropped to the bottom thereof The formation is then often stimulated by any one of a number of well-known means to enhance production of hydrocarbons therefrom.
Examples of the known perforating devices can be found in U.S. Pat. Nos. 4,538,680 to Brieger et al; U.S. Pat. No. 4,619,333 to George; U.S. Pat. No. 4,768,597 to Lavigne et al; U.S. Pat. No. 4,790,383 to Savage et al; U.S. Pat. No. 4,911,251 to George et al; U.S. Pat. No. 5,287,924 to Burleson et al; U.S. Pat. No. 5,423,382 to Barton et al; and U.S. Pat. No. 6,082,450 to Snider et al. All of these relate to perforating guns which are lowered within a casing string carrying explosive charges which are detonated to perforate the casing outwardly. This had the advantage of leaving the inside of the casing relatively unobstructed since debris and ragged edges would be outwardly directed by the detonations of the charges.
In the late 1990s, successes were found with casing conveyed perforating guns in which the guns and control lines were attached to the outside of the casing. One disadvantage of this approach is that the externally conveyed elements are subject to damage during normal run-in operations. A second disadvantage is the perforations leaving ragged shards extending inwardly causing obstructions on the inside of the casing.
PCT application PCT/US00/05774, to Snider et al, describes another attempt to perforate a tubular from the outside. This differs from the above mentioned perforating from the outside of the casing in that Snider et al propose a perforating gun separate from and exterior to the casing to be perforated. When the Snider et al perforating gun is detonated, portions of the gun act in a manner similar to shrapnel to perforate the casing string. This is not a satisfactory solution to the problem of perforating tubulars in that it raises the possibility of a very ragged perforating which could easily destroy the structural integrity of the casing string, particularly in view of the fact that it utilizes portions of the casing itself to perforate the side of the casing furthest from the perforating gun. This can also result in a ragged inner surface of the casing which could damage or prevent passage of downhole tools and instruments. Perforating a casing from the inside raised this consideration to a much lesser degree.
Frequently a well penetrates multiple zones of the same formation and/or a plurality of hydrocarbon bearing formations of interest. It is usually desirable to establish communication with each zone and/or formation of interest for injection and/or production of fluids. Conventionally, this has been accomplished in any one of several ways. One way is to use a single perforating gun which is conveyed by wireline or tubing into the well bore and an explosive charge fired to perforate a zone and/or formation of interest. This procedure is then repeated for each zone to be treated and requires running a new perforating gun into the well for each zone and/or formation of interest. One alternative is to have a single perforating gun carrying multiple explosive charges. This multiple explosive charge gun is conveyed on wireline or tubing into the well and, as the gun is positioned adjacent to each zone and/or formation of interest, selected explosive charges are fired to perforate the adjacent zone and/or formation. In another alternative, two or more perforating guns, each having at least one explosive charge, are mounted spaced apart on a single tubing, then conveyed into the well, and each gun is selectively fired when positioned opposite a zone and/or formation of interest. When the select firing method is used, and the zone and/or formation of interest are relatively thin, e.g., 15 feet or less, the perforating gun is positioned adjacent the zone of interest and only some of the shaped charges carried by the perforating gun are fired to perforate only this zone or formation. The gun is then repositioned, by means of the tubing, to another zone or formation and other shaped charges are fired to perforate this zone or formation. This procedure is repeated until all zones and/or formations are perforated, or all of the shaped explosive charges detonated, and the perforating gun is retrieved to the surface by means of the tubing.
However, the necessity of tripping in and out of the well bore to perforate and stimulate each of multiple zones and/or formations is time consuming and expensive. In view of this, multiple zones and/or formations are often simultaneously stimulated, even though this may result in certain zones and/or formations being treated in a manner more suitable for an adjacent zone and/or formation. Thus a need exists for apparatus and processes to perforate casing which is positioned within a well bore which eliminates the need to run perforating equipment in and out of the well when completing multiple zones and/or formations.
Disadvantages of the presently known methods of perforating are several, including: the perforating device itself may need to be retrieved; and the cabling systems to convey signals to the charges must be carried outside or inside the tubulars, either subjecting the cabling system to damage and/or taking up space. Protective means, such as wraparound metal protectors, armored cable housings, or grooved casing couplings, must be used to avoid damaging externally mounted cabling systems, explosive charges and their respective detonating means. In order to perforate the adjacent formation, internally conveyed or mounted perforating systems necessarily also perforate the tubular within which they are conveyed which in certain instances, such as when trying to relieve annular pressure, is undesirable.
Accordingly, it is an object of the present invention to provide a method and apparatus for economically and effectively perforating and stimulating multiple zones and/or formations which are penetrated by a well.
It is another object of the present invention to provide a process and apparatus for completing a well wherein the casing is perforated to provide for fluid communication through the wall of the casing by means of a perforating gun assembly forming a portion of the casing string.
It is a further object of the present invention to provide a method and apparatus for completing and stimulating a cased well bore wherein shaped explosive charges are mounted in contact with, or at least partially embedded in, the casing wall so that a precise hole is formed without undue damage to the casing or unwanted internally directed projections left to interfere with passage of tools and/or instrumentation through the casing.
It is a still further object of the present invention to provide a method and apparatus for completing and stimulating a cased well bore wherein each shaped explosive charge is at least partially embedded in the casing wall so that a precise hole is formed without undue damage to the casing or unwanted internally directed projections left to interfere with passage of tools and/or instrumentation through the casing.
It is still another object of the present invention to provide a method for perforating a casing utilizing wireless communication from the surface to initiate detonation of the respective explosive charges of the perforating assembly, the wireless communication employing coded signaling to prevent errors in detonation.
The present invention provides a method and apparatus for perforating a well casing without the disadvantages of known perforating tools. The present apparatus for perforating a well casing comprises: a tubular having coaxial outside and inside surfaces with a closed wall extending therebetween; at least one explosive charge in contact with the outside surface of the wall of the tubular; at least one detonation device in communication with the at least one explosive device; at least one programmable logic interface to arm and fire the detonation device; and a control station in wireless and cableless communication with the at least one programmable logic interface whereby a coded signal from the control station is received by the logic interface to detonate the at least one explosive charge.
The present invention also provides a method for perforating a well bore, the method comprising the steps of providing a well bore; running a tubing string down the well bore, wherein said tubing string comprises at least one perforating tubular having coaxial outside and inside surfaces with a wall extending therebetween; providing at least one explosive charge in contact with the outside surface of the wall; providing at least one detonation device in communication with the at least one explosive charge; providing at least one programmable logic interface to arm and fire the detonation device; providing a control station in wireless and cableless communication with at least one of the at least one programmable logic interface; lowering the production tubing string until the at least one perforating tubular is adjacent to a predetermined zone to be perforated; sending a coded wireless signal from the control station to the at least one programmable logic interface to arm and fire at least one detonation device thereby detonating at least one explosive charge and perforating the well bore and, optionally, at least one perforating tubular; and producing liquids, gases, or a combination thereof through the production tubing string.
The method can also be used for venting annular pressure in a well bore by the steps of providing a well bore; providing a casing string having at least one self-perforating tubing with coaxial outside and inside surfaces with a wall extending therebetween; providing at least one explosive charge in direct contact with or at least partially penetrating the outside surface; providing at least one detonation device in communication with the at least one explosive charge; and providing at least one programmable logic interface to arm and fire the at least one detonation device; running the casing string into the well bore; providing a production tubing having an outside surface; running production tubing inside the casing thereby forming an annular space between the outside surface of the production tubular and the inside surface of the casing; providing a control station in wireless and cableless communication with at least one of the at least one programmable logic interfaces; and sending a coded wireless signal from the control station to the at least one least one programmable logic interface to detonate at least one explosive charge thereby perforating at least one self-perforating casing and the well bore, but not the production tubular; and allowing pressure to vent from the annular space to the formation via the now perforated casing.